At least five people have been killed in two separate explosions in the north-east Indian state of Assam.

Police say three people were killed when suspected militants set off a bomb on board a bus carrying Indian border police in Goalpara.

Earlier, two people were killed and more than 30 injured in a bomb blast on a passenger bus in Gossaigaon.

There have been four blasts in less than 12 hours in Assam blamed on separatist militants.

Daughter dead

In the latest attack, a senior official of the Border Security Force told the BBC that suspected rebels of the United Liberation Front of Assam (Ulfa) may have placed a bomb on board a bus carrying BSF personnel and their families going on leave.

One of the people killed was the daughter of a BSF constable.

Passengers spotted an unidentified sack inside the bus and as they were trying to disembark, the explosion took place, blowing apart the vehicle

Ashish BhutaniLocal official

Earlier, an explosion ripped through a passenger bus as it was passing the town of Gossaigaon, 270 kilometers (167 miles) west of Assam's main city of Guwahati.

The bus was travelling from the western town of Dhubri to Cooch Behar in the neighbouring West Bengal.

"Passengers spotted an unidentified sack inside the bus and as they were trying to disembark, the explosion took place, blowing apart the vehicle," a local official, Ashish Bhutani, told the AFP news agency.

Doctors say the toll could rise as the some of the victims are in a serious condition.

Series of attacks

Similar attacks in the past have been blamed on separatist rebels and police say they could have carried out this one as well.

"It is possible that Ulfa militants had left a timed device inside the bus," Assam's Inspector General of Police Khagen Sharma told the Associated Press.

Late on Wednesday, suspected ULFA rebels threw a grenade outside a cinema hall in the
town of Dibrugarh, killing one person.

Around the same time, suspected militants set off an improvised explosive devise on a railway line in Assam's Kokrajhar district, disrupting railway traffic.

Eighteen people, mostly women and children, were killed in a bomb explosion in the town of Dhemaji during an Independence Day march earlier this month.

Police blamed the attack on one of Assam's eight separatist groups.

Rebels in Assam have been fighting for independence since 1979 in a struggle which has claimed more than 10,000 lives.

The United Liberation Front of Assam (Ulfa) had called for a boycott of Independence Day events.